CODEWITHSUNDEEP
cstringfile-iolong-integer
Maheen Siddiqui
Maheen Siddiqui

Reputation: 185

Reading the number of entries in a data file in C

I am trying to write a C program that reads how many lines/entries there are in a set data file. I have used the code below and it works fine (gotten from: What is the easiest way to count the newlines in an ASCII file?)

#include <stdio.h>

int main()
{
FILE *correlations;
correlations = fopen("correlations.dat","r");
int                 c;              /* Nb. int (not char) for the EOF */
unsigned long       newline_count = 0;

    /* count the newline characters */
while ( (c=fgetc(correlations)) != EOF ) {
    if ( c == '\n' )
        newline_count++;
}

printf("%lu newline characters\n", newline_count);
return 0;
}

But I was wondering if there was a way to change this bit 

if ( c == '\n' )
        newline_count++;

into something else so that if your data looks like

1.0

2.0

3.0

(with an entry then the new line is a space then an entry then space) instead of 

1.0
2.0
3.0

How do I get it to differentiate between a character/string/integer and just a new line? I tried %s but it didn't work.. I am just trying this out first on a small file with only 3 entries, but I will be using a very big file later on where I have spaces between each line so I'm wondering how to differentiate... Or should I divide the line_count by 2 to get the number of entries?

Upvotes: 1

Views: 422

Answers (1)

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726579

You can make a flag that tells you that you saw at least one non-whitespace character after the last \n, so that you could increment the line counter only when that flag is set to 1:

unsigned int sawNonSpace = 0;
while ( (c=fgetc(correlations)) != EOF ) {
    if ( c == '\n' ) {
        newline_count += sawNonSpace;
        // Reset the non-whitespace flag
        sawNonSpace = 0;
    } else if (!isspace(c)) {
        // The next time we see `\n`, we'll add `1`
        sawNonSpace = 1;
    }
}
// The last line may lack '\n' - we add it anyway
newline_count += sawNonSpace;

Dividing the count by two is not reliable, unless you are guaranteed to have double spacing in all your files.

Upvotes: 1

Related Questions